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Scientists often favor male specimens over female ones, the National Institutes of Health said this week.
Spencer Platt/Getty Images

N.I.H. says sex bias in studies makes research less effective for women

Government research body says bias for male test specimens may undermine drug efficacy, increase side effects for women

May 14, 20146:37PM ET

The U.S. government's medical research agency is taking steps to erase gender bias in biomedical studies, saying scientists too often use male lab animals and cells — which can mask the way men and women react differently to some drugs.

Beginning Oct. 1 of this year, researchers seeking grants from the National Institutes of Health (NIH) must report their plans for balancing male and female cells and animals in preclinical studies, with only “rigorously defined exceptions,” the NIH announced Wednesday.

The NIH also plans to train grant recipients and its own staff in designing studies without sex bias.

The new requirement is likely to have a big influence on research because the agency is one of the world's top financial backers of biomedical studies, spending about $30 billion annually.

"Our goal is to transform how science is done," wrote NIH Director Francis Collins and Janine Clayton, director of the NIH Office of Research on Women's Health, in the science journal Nature.

The current overreliance on male laboratory animals, including mice and rats, and on male cells in lab dishes obscures important differences that could guide future studies involving human subjects and can lead to flawed findings, the NIH said.

Overrelying on male specimens can obscure differences in how women and men react even to common drugs such as aspirin. That can lead to women having more complications with many medications.

Studies have shown that women experience more severe side effects from new drug treatments, according to The New York Times. The Food and Drug Administration last year advised that women should take only half their prescribed dose of Ambien, a common sleeping pill, because of new studies showing that they metabolized the drug differently than men.

The agency said inadequate inclusion of female cells and animals and inadequate analysis of data by gender may also contribute to a "troubling rise" in findings by researchers that other researchers are then unable to verify in separate studies.

Twenty-one years ago, the agency began requiring inclusion of women in NIH-funded research using human subjects. Previously, some studies that were used to determine whether a new medicine or treatment worked simply excluded women.

Before new medicines or treatments can be tried on human subjects, they are tested on animals or cells in a lab. These preclinical studies can lead to human clinical trials.

"I really think this is a blind spot. I don't know that there's intentional bias here. But there's certainly a reliance on male-only animal models, which have become the convention in some fields," Clayton said in an interview with Reuters.

Clayton said the imbalance stems in part from an obsolete notion that the female hormonal cycle would cause too much variability in lab animals and disrupt a study's results.

Scientists who have studied gender imbalance in this research welcomed the NIH move.

"Males get treated as the default experimental subject. If you try to publish a study using only females, you typically have to justify your reasoning — but few people blink at male-only studies," said Annaliese Beery, a neuroscientist at Smith College.